Turn the trimmer over and locate the trimmer reel at the end of the trimmer shaft.
Locate the hole in the trimmer shaft just below the trimmer reel. Rotate the real until the hole in the gear set and the shaft line up.
Place an Allen wrench into the hole to lock the shaft in place.
Turn the reel clockwise to loosen it. Thread the reel off the trimmer shaft. Keep in mind that the threads are reversed on the trimmer reel.
Place the new trimmer reel onto the shaft and thread it counterclockwise into place. Turn hard on the reel to tighten it on the shaft.
Pull the Allen wrench from the trimmer's shaft.